Exactly, that's the appeal of Street Mod for me. I can do pretty much anything I ever wanted to my Sube and it fits within the class. My RB5 Prodrive wing is the only "mod" that probably makes me slower.

To follow-up on Eric's note about the suspension mods, you must use the stock mounting points on the frame or unibody. As long as you're not drilling new holes into the frame, it's legal.
Moreover, all the typical Turbo/SC electronics are legal too. If I remember correctly, the only drivetrain stuff that starts to get you into trouble (of the stuff I remember from this board) are non-stock injectors or fuel pump. This next statement may end up confusing the issue, but as of today any production *Subaru* engine part would be a legal install. I haven't quite figured out if 22b like parts from Subaru would be legal. Anyone else know?

There is SOME ambuguiy about bumpers, but the intent is clear. Most of the stuff on your car (except for quarter panels, windows, doors, and the trunk) can be replaced with any off the shelf part. As long as the bumper swap is "technically" a bumper, it's legal.